Fluid-actuated punch press with workpiece stripper

ABSTRACT

The press includes a fluid-operated actuator for reciprocating a punch and also includes a stripper which is partially telescoped into the cylinder of the actuator so as to be forced downwardly into clamping engagement with the workpiece by the same pressure fluid admitted into the cylinder to retract the punch upwardly out of the workpiece. In addition, the actuator and a spring disposed within the cylinder coact to cause the stripper to clamp the workpiece during punching and to release the workpiece after the punch has been retracted out of the workpiece.

United States Patent [1 1 Brolund et al.

[ 51 Mar. 27, 1973 [s41 FLUID-ACTUATED PUNCHPRESS wmr WORKPIECE STRIPPER [75] Inventors: Theodore F. Brolund, Rockford, 111.; William E. Kuchar, Cherry Valley,

111. 73 Assignee: w. A. Whitney Corp., Rockford, m,

[22] Filed: Dec. 31, 1970 21 Appl. No.: 103,025

[52] US. Cl. ..83/137, 83/140, 83/462 [51] Int. Cl. ..B26d 7/06 [58] Field of Search ..83/l37, 140, 142, 143, 461,

[5 6] References Cited UNITED STATES PATENTS 8/1955 Taylor ..83/l37 4/1954 Griswold ..83/l40 X 3,205,742 9/1965 Williamson ..83/14O 3,461,762 8/1969 Deni et al. .....83/l43 2,118,648 5/1938 Johnson ..83/l37 Primary Examiner-Andrew R. J uhasz Assistant Examiner-Leon Gilden Attomey--Wolfe, Hubbard, Leydig, Voit & Osann [57] ABSTRACT The press includes a fluid-operated actuator for reciprocating a punch and also includes a stripper which is partially telescoped into the cylinder of the actuator so as to be forced downwardly into clamping engagement with the workpiece by the same pressure fluid admitted into the cylinder to retract the punch upwardly out of the workpiece. In addition, the actuator and a spring disposed within the cylinder coact to cause the stripper to clamp the workpiece during punching and to release the workpiece after the punch has been retracted out of the workpiece.

3 Claims, 4 Drawing Figures PATENTEDHARZYIQYS 722,337

sum 10? 2 FLUID-ACTUATED PUNCH PRESS WITH WORKPIECE STRIPPER BACKGROUND OF THE INVENTION This relates to a punch press for perforating a workpiece and, more particularly, to a press of the type in which a punch is attached to the free end of the ram of a double-acting, fluid-operated actuator and is advanced and retracted in response to the admission of pressure fluid alternately into opposite ends of the cylinder of the actuator. Usually, such a press includes a stripper which is telescoped over the punch to engage the workpiece as the punch is retracted thereby to strip the workpiece cleanly off of the punch at the completion of each punching operation.

SUMMARY OF THE INVENTION The general aim of the present invention is to provide a new and improved press of the above character in which the pressure fluid admitted into the cylinder to retract the punch and the ram is utilized to additional advantage to force the stripper into tight and positive clamping engagement with the workpiece so as to prevent any movement of the workpiece with the punch during retraction of the latter.

A more detailed object is to achieve the foregoing in a simple manner by telescoping the stripper slidably into the ram end of the cylinder so that the stripper will be forced automatically into pressing engagement with the workpiece when .the ram end of the cylinder is pressurized to retract the ram and the punch.

The invention further resides in the unique mounting of the stripper and in the novel coaction between the stripper and the fluid-operated actuator so as to cause the stripper to clamp the workpiece at the-beginning of and during punching, to cause the stripper to remain in tight clamping engagement with the workpiece during retraction of the punch from the workpiece, and to effect retraction of the stripper away from the workpiece as an incident to continued retraction of the punch so as to free the workpiece for re-positioning.

These and other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a new and improved punch press embodying the novel features of the present invention, parts of the press being broken away and shown in section.

FIGS. 2 and 3 are fragmentary views similar to FIG. 1 but showing certain parts of the press in moved positions and illustrating successive steps occurring during an operating cycle.

FIG. 4 is an enlarged cross-section taken along the line 4--4 of FIG. 2.

DETAILED DESCRIPTION OF THE'PREFERRED EMBODIMENT As shown in the drawings for purposes of illustration, the invention is embodied in a punch press having a double-acting fluid-operated actuator 11 mounted on a C-shaped support or frame 13 and operable to reciprocate a punch 14 through downward and upward strokes relative to a die 15 on the frame so as to punch a hole in a workpiece 16 such as a piece of sheet metal disposed between the punch and the die. The press is supported on a bed 17 and has been illustrated as operating in an upright position although it should be realized that the press could be oriented angularly on the bed to operate on workpieces of various types and shapes.

In this instance, the actuator 11 is mounted on an upper arm 19 of the frame 13 and comprises a cylinder 20 within which a piston 21 slides downwardly and upwardly in response to the admission of pressure fluid such as hydraulic oil alternately into upper and lower chambers 23 and 24 within the upper and lower ends of the cylinder, the pressure fluid being controlled by a valve (not shown) and being delivered to and dumped from the chambers through conduits 25 and 26 communicating with a suitable pressure source by way of the valve. The cylinder includes an integral sleeve 27 projecting downwardly into an opening 29 in the arm 19, and is connected to the arm by bolts 30 which also serve to anchor a cap 31 to the upper end of the cylinder. Projecting downwardly from the piston and telescoped into the sleeve is a rod or ram 33 whose lower or free end carries the punch 14. Thus, when pressure fluid is admitted into the upper chamber 23 (i.e., the head end of the cylinder), the piston and the ram are forced downwardly to drive the punch through the workpiece l6 and, when pressure fluid is admitted into the lower chamber 24 (i.e., the ram end of the cylinder), the.piston and the ram are shifted upwardly to retract the punch out of the workpiece.

As the punch 14 is retracted upwardly from the workpiece 16 at the completion of the punching operation, a stripper 35 coaxial with the punch engages the upper surface of the workpiece to strip the latter off of the punch. The stripper thus holds the workpiece during retraction of the punch so that the punch may be free itself from its close fit with the edges of the hole punched in the workpiece.

In accordance with the present invention, the pressure fluid admitted into the lower chamber 24 of the cylinder 20 is utilized not only to retract the punch 14 upwardly out of the workpiece 16 but also to force the stripper 35 downwardly into tight pressing engagement with the workpiece thereby to keep the latter clamped tightly against the die 15 during retraction of the punch and to lock the workpiece against any upward movement whatsoever. Moreover, the stripper is arranged to clamp the workpiece at the start of and during punching as well as during initial retraction of the punch and then is released from the workpiece as the punch moves to a fully retracted position so that the workpiece may be re-positioned beneath the punch for punching of another hole.

In the present instance, the stripper 35 includes a tubular upper end portion 36 which is telescoped slidably over the ram 33 and which also is telescoped slidably into the sleeve 27 on the lower end of the cylinder 20. The extreme upper end 37 of the stripper is disposed within the lower chamber 24 and thus is positioned to be exposed directly to and acted upon by the pressure fluid admitted into the lower chamber. Accordingly, when the lower chamber is pressurized to raise the piston 21 and retract the punch 14 upwardly, a downward reaction force is exerted on the upper end of the stripper and tends to shift the stripper downwardly away from the piston and downwardly of the lower end of the cylinder. An O-ring 39 seals the inner surface of the stripper 35 to the outer surface of the ram 33 while an O-ring 40 seals the outer surface of the stripper to the inner surface of the sleeve 27 to maintain the lower chamber 24in a fluid-tight condition.

For a purpose to be explained more fully subsequently, a coil spring 41 telescoped over the upper end portion of the ram 33 is fitted into a counterbore 43 formed in the upper end portion 36 of the stripper 35 and is compressed between the bottom of the counterbore and the lower end of the piston 21. The spring urges the stripper downwardly of the cylinder 20 with such downward movement being limited by an annular abutment or collar 44 attached to the ram approximately midway between its ends. The upper surface of the collar is positioned to be engaged by an internal shoulder 45 formed within the stripper by counterboring the lower end portion of the stripper. Downwardly of the shoulder 45, diametrically opposed and axially extending slots are formed through the tubular wall of the stripper and thus the lower end portion of the stripper is defined by two opposed and substantially arcuate fingers 50 (see FIG. 4) whose lower ends are disposed adjacent the punch 14 to engage and clamp against the workpiece 16.

At the beginning of each punching cycle, the piston 21 is retracted fully within the cylinder 20 and is disposed at the top of the upper chamber 23 as shown in FIG. 1. The ram 33 thus is in a retracted position with the collar 44 engaging the shoulder 45 and holding the stripper 35 upwardly within the sleeve 27 against the force exerted by the spring 41 which initially is compressed to a certain degree. Accordingly, the fingers 50 and the punch 14 are retracted upwardly from the workpiece 16 with the lower end of the punch being at the same level as the lower ends of the fingers (see FIG. 1).

When the upper chamber 23 is pressurized, the piston 21 is advanced downwardly to drive the punch 14 downwardly toward the workpiece 16. During initial advancement of the piston, the spring 41 acts as a rigid link between the piston and the stripper 35 to force the latter to move downwardly in unison with the punch, the shoulder 45 remaining in engagement with the collar 44 during such movement.

The punch 14 and the fingers 50 engage the workpiece 16 at the same time as shown in FIG. 2 and, as the punch penetrates the workpiece, the fingers clamp the workpiece against the die and help keep the workpiece in a stationary position during the downward punching stroke. As soon as the fingers 50 engage the workpiece, the spring 41 compresses and yields to allow the punch to continue to advance downwardly relative to the stripper 35, the latter being held stationary as a result of the fingers engaging the workpiece (see FIG. 3). The punch thus is driven through the workpiece upon continued advancement of the ram 33 and, as an incident thereto, the collar 44 moves downwardly away from the shoulder 45.

After the punch 14 has been driven completely through the workpiece 16, pressure fluid is dumped from the upper chamber 23 and is delivered into the lower chamber 24 to begin retracting the piston 21 and the punch. At the same time, the pressure fluid in the lower chamber exerts a substantial downward force on the upper end 37 of the stripper 35 and serves to hold the fingers 50 in tight clamping engagement with the workpiece (see FIG. 3). Accordingly, during retraction of the punch from the workpiece, the fingers lock the workpiece tightly against the die 15 as shown in FIG. 3 and strip the workpiece from the punch without allowing any upward movement of the workpiece whatsoever. Thus, it will be appreciated that the fluid pressure in the lower chamber keeps the stripper pressed tightly downwardly against the workpiece as the punch retracts and as the force exerted on the stripper by the relaxing spring 41 decreases during such retraction.

As soon as the lower end of the punch 14 clears the workpiece 16, the collar 44 picks up and engages the shoulder 45 (see FIG. 2) so that, with continued retraction of the punch, the stripper 35 is retracted upwardly from the workpiece-to free the latter for re-positioning under the punch. Thus, the stripper is spaced upwardly from the workpiece as shown in FIG. 1 when the piston 21 reaches the top of the cylinder 20 in position to begin the next punching cycle.

From the foregoing, it will be apparent that the present invention brings to the art a new and improved punch press 10 with a stripper 35 which is pressed into clamping engagement with the workpiece 16 by the same pressure fluid which serves to retract the punch 14. The workpiece thus is clamped securely as a result of the fluid pressure and yet there is no need to incorporate additional valving into the machine to control the stripper. The actuator 11 also coacts with the spring 41 to cause the stripper to clamp the workpiece during punching and to release the workpiece after the punch has been retracted.

We claim as our invention:

1. A punch press comprising a support, a double-acting, fluid-operated actuator on said support and comprising a cylinder with a piston slidable downwardly and upwardly therein in response to the admission of pressure fluid alternately into upper and lower chambers in the upper and lower ends of said cylinder, a ram projecting downwardly from said piston and guided for up and down sliding by said cylinder, and a punch supported on the lower end of said ram and cooperable with an underlying die on said support to perforate an intervening workpiece on the downward stroke of said ram, the improvement in said press comprising, a stripper telescoped slidably over said ram and having a lower end spaced upwardly from the workpiece when the ram is fully retracted, a mechanical spring acting on said stripper and operable during the downward stroke of said ram first to move said stripper downwardly with the ram and into engagement with said workpiece and thereafter to permit continued advancement of said ram relative to said stripper to drive said punch through said workpiece, the upper end portion of said stripper being telescoped slidably into the lower end of said cylinder and being disposed within said lower chamber whereby pressure fluid admitted into said lower chamber during initial upward retraction of said ram exerts a downward force on the stripper to keep the latter in clamping engagement with said workpiece,

being compressed when said stripper engages said 1 workpiece during the downward stroke of said ram and yielding to permit continued downward advancement of the ram relative to the stripper.

3. A punch press as defined in claim 1 further including means disposed within said cylinder and sealing said stripper to the outer surface of said ram to the inner surface of said cylinder to keep said lower chamber fluid-tight. 

1. A punch press comprising a support, a double-acting, fluidoperated actuator on said support and comprising a cylinder with a piston slidable downwardly and upwardly therein in response to the admission of pressure fluid alternately into upper and lower chambers in the upper and lower ends of said cylinder, a ram projecting downwardly from said piston and guided for up and down sliding by said cylinder, and a punch supported on the lower end of said ram and cooperable with an underlying die on said support to perforate an intervening workpiece on the downward stroke of said ram, the improvement in said press comprising, a stripper telescoped slidably over said ram and having a lower end spaced upwardly from the workpiece when the ram is fully retracted, a mechanical spring acting on said stripper and operable during the downward stroke of said ram first to move said stripper downwardly with the ram and into engagement with said workpiece and thereafter to permit continued advancement of said ram relative to said stripper to drive said punch through said workpiece, the upper end portion of said stripper being telescoped slidably into the lower end of said cylinder and being disposed within said lower chamber whereby pressure fluid admitted into said lower chamber during initial upward retraction of said ram exerts a downward force on the stripper to keep the latter in clamping engagement with said workpiece, and an abutment on said ram and engageable with said stripper upon continued upward retraction of the ram thereby to retract the stripper upwardly from the workpiece.
 2. A punch press as defined in claim 1 in which said spring comprises a coiled compression spring telescoped over said ram and urging said stripper downwardly and away from said piston, said spring being compressed when said stripper engages said workpiece during the downward stroke of said ram and yielding to permit continued downward advancement of the ram relative to the stripper.
 3. A punch press as defined in claim 1 further including means disposed within said cylinder and sealing said stripper to the outer surface of said ram to the inner surface of said cylinder to keep said lower chamber fluid-tight. 